This invention relates to immobilised biological entities, surfaces, and solid objects, for example medical devices, coated with such entities, and processes and intermediates for their production.
When a medical device is placed in the body, or in contact with body fluids, a number of different reactions are set into motion, some of them resulting in the coagulation of the blood in contact with the device surface. In order to counteract this serious adverse effect, the well-known anti-coagulant compound heparin has for a long time been administered systemically to patients before the medical device is placed in their body, or when it is in contact with their body fluids, in order to provide an antithrombotic effect.
Thrombin is one of several coagulation factors, all of which work together to result in the formation of thrombi at a surface in contact with the blood. Antithrombin (also known as antithrombin III) (“AT”) is the most prominent coagulation inhibitor. It neutralizes the action of thrombin and other coagulation factors and thus restricts or limits blood coagulation. Heparin dramatically enhances the rate at which antithrombin inhibits coagulation factors.
However, systemic treatment with high doses of heparin is often associated with serious side-effects of which bleeding is the predominant. Another rare, but serious complication of heparin therapy is the development of an allergic response called heparin induced thrombocytopenia that may lead to thrombosis (both venous and arterial). High dose systemic heparin treatment e.g. during surgery also requires frequent monitoring of the activated clotting time (used to monitor and guide heparin therapy) and the corresponding dose adjustments as necessary.
Therefore solutions have been sought where the need for a systemic heparinisation of the patient would be unnecessary or can be limited. It was thought that this could be achieved through a surface modification of the medical devices using the anti-coagulative properties of heparin. Thus a number of more or less successful technologies have been developed where a layer of heparin is attached to the surface of the medical device seeking thereby to render the surface non-thrombogenic. For devices where long term bioactivity is required, heparin should desirably be resistant to leaching and degradation.
Heparin is a polysaccharide carrying negatively charged sulfate and carboxylic acid groups on the saccharide units. Ionic binding of heparin to polycationic surfaces was thus attempted, but these surface modifications suffered from lack of stability resulting in lack of function, as the heparin leached from the surface.
Thereafter different surface modifications have been prepared wherein the heparin has been covalently bound to groups on the surface.
One of the most successful processes for rendering a medical device non-thrombogenic has been the covalent binding of a heparin fragment to a modified surface of the device. The general method and improvements thereof are described in European patents: EP-B-0086186, EP-B-0086187, EP-B-0495820 and U.S. Pat. No. 6,461,665.
These patents describe the preparation of surface modified substrates by first, a selective cleavage of the heparin polysaccharide chain, e.g. using nitrous acid degradation, leading to the formation of terminal aldehyde groups. Secondly, the introduction of one or more surface modifying layers carrying primary amino groups on the surface of the medical device, and thereafter reacting the aldehyde groups on the polysaccharide chain with the amino groups on the surface modifying layers followed by a reduction of the intermediate Schiff's bases to form stable secondary amine bonds.
DE 19604173 relates to medical devices with a polymer surface based on a substituted bis-phenyl monomer to which a pharmaceutically active agent such as heparin may be attached.
WO 2008/090555 relates to a medical device coated with a polymer matrix which incorporates a pharmaceutically active agent. It appears that the active agent may be incorporated within the polymer matrix.
U.S. 2005/0059068 relates to a chemically active surface able to covalently react with substances containing a hydroxyl group and/or an amine group, comprising a solid surface having an activated dendrimer polyamine covalently bonded to said surface through a silane containing reagent, wherein the dendrimer polyamine can covalently bind the substance comprising a hydroxyl group and/or an amine group.
However there is still a requirement for surface modifications that can be performed under mild conditions (e.g. which do not degrade the heparin) which are more easily manipulated, are simpler and more efficient to produce and/or where the bioavailability of the heparin moiety is higher.
Our earlier application WO 2010/029189 relates to a medical device having a coating with an anticoagulant molecule such as heparin covalently attached to the coating via a 1,2,3-triazole linkage. The document describes the azide or alkyne functionalisation of a polyamine; the preparation of alkyne or azide functionalised heparin (both native and nitrous acid degraded heparin); and the reaction to link the derivatised heparin to the derivatised polymer via a 1,2,3-triazole linker.
We have now found a further simple method of covalently attaching entities capable of interacting with mammalian blood to prevent coagulation or thrombus formation, e.g. heparin, and especially full length heparin rather than the degraded heparin of the prior art, to a surface.